Plane trigonometry, by S.L. Loney.

202

TRIGONOMETRY.

We first measure an angle ABD equal to the given
angle B.
A A
'........
B < jD D
Fig. 1 Fig. 2
A A
C b b b..... b
B Ci C B D
Fig. 3
We then measure along BA a distance BA equal to
the given distance c, and thus determine the angular
point A.
We have now to find a third point C, which must lie
on BD and must also be such that its distance from A
shall be equal to b.
To obtain it, we describe with centre A a circle whose
radius is b.
The point or points, if any, in which this circle meets
BD will determine the position of C.
Draw AD perpendicular to BD, so that
AD = AB sin B = c sin B.
One of the following events will happen.
The circle may never reach BD (Fig. 1) or it may